Pulse photodynamic treatment of skin conditions

ABSTRACT

A pulse photodynamic therapy (or pulse PDT) treatment of skin complaints is described herein. The skin complaint being treated can be actinic keratosis (AK) or a basal cell carcinoma (BCC).

FIELD OF THE INVENTION

The present invention is related to a pulse photodynamic therapy (or pulse PDT) treatment of skin complaints, wherein the skin complaint is selected in the group consisting of actinic keratosis (AK) and a basal cell carcinoma (BCC).

BACKGROUND OF THE INVENTION

Actinic keratosis (AK) is a hyperkeratotic pre-cancerous epidermal lesion that is known to be caused by frequent and chronic exposure of the skin to sunlight. The condition typically presents as small, rough patches of skin approximately 2 mm to 7 mm in diameter. The patches are usually reddish in color, with rough texture and whitish or yellow hyperkeratosis. Actinic keratosis maybe unpleasant or even painful, and untreated may develop to a malignant tumor (squamous cell carcinoma) Actinic keratosis is most commonly treated with topical treatments such photodynamic therapy (ALA, 5-MAL and HAL as photosensitizers)), imiquimod, diclofenac, or 5-fluorouracil, especially when patients present with multiple lesions or so called field cancerisation. Alternatively, the condition may be treated by cryosurgery with liquid nitrogen or even curettage especially when patients present with few lesions. Surgery is recommended when there is a suspicion of invasive SCC.

Basal cell carcinoma is the most common form of skin cancer and accounts for more than 90% of all skin cancer in the U.S. These cancers almost never spread (metastasize) to other parts of the body, although they can cause damage by growing and invading surrounding tissue.

Basal cell carcinomas usually present initially as a small, dome-shaped nodule often pearl like shiny and translucent and with superficial blood vessels. Some basal cell carcinomas contain melanin pigment, making them look dark rather than shiny.

Photodynamic therapy (PDT), is a technique for the treatment of various abnormalities or disorders of the skin or other epithelial organs or mucosa, especially cancers or pre-cancerous lesions, as well as certain non-malignant lesions (e.g. skin complaints such as psoriasis, actinic keratosis (AK) and acne). PDT involves the application of photosensitizing (photochemotherapeutic) agents to the affected area of the body, followed by exposure to photoactivating light in order to activate the photosensitizing agents and convert them into cytotoxic form, whereby the affected cells are killed (necrosis, apoptosis).

A range of photosensitizing agents is known, including the psoralens, the porphyrins (e.g. Photofrin (Registered trademark)), the chlorins and the phthalocyanins. Amongst the most clinically useful photosensitizing agents known in the art, however, are 5-aminolevulinic acid and its derivatives, for example esters such as 5-ALA esters.

The mechanism of action of PDT relies on intracellular porphyrins (including PpIX) that are photoactive, fluorescing compounds and, upon light activation in the presence of oxygen, singlet oxygen is formed which causes damage to cellular compartments, in particular the mitochondria. Light activation of accumulated porphyrins leads to a photochemical reaction and thereby phototoxicity to the light-exposed target cells.

Although PDT is clinically useful in the treatment of a wide range of diseases, a major drawback of such treatment is the concomitant side-effects, particularly at the treatment site. These often include inflammation such as erythema, swelling, edema, burning, itching, exfoliation, hyperpigmentation and prolonged irritation and hypersensitivity after treatment. Such side-effects are particularly undesirable when the treatment site is the face, scalp or neck. This is frequently the case when the PDT is for the treatment of lesions (e.g. acne, basal cell carcinoma, actinic keratosis, photodamage and Bowen's disease (BD)).

The occurrence of such side effects is recognized in WO2006/051269 which discloses use of 5-ALA esters in PDT for the treatment of acne. WO2006/051269 describes a study wherein a cream comprising 16% wt. methyl ALA ester is applied to the faces of subjects for 3 hours followed by exposure of the subjects' faces to non-coherent red light (light dose 37 Jkm-2). The treatment was then repeated 2 weeks later. Although the results confirmed that PDT with methyl ALA ester is effective in the treatment of acne, the subjects also indicated that the treatment caused pain and induced severe inflammation.

WO02/13788 discloses a similar study on use of ALA acid in PDT for the treatment of acne. In this case 20% ALA acid was applied to the backs of the subjects for 3 hours and then the subjects were exposed to 150 J/cm2 broad band light. Again the results confirmed that PDT with ALA is effective for the treatment of acne, but the subjects also reported a plethora of undesirable side effects. For example, WO02/13788 reports that erythema, hyperpigmentation and exfoliation were often seen after PDT treatment and states that in some cases a subsequent treatment even had to be postponed. Reports of pain, burning and itching during and after treatment were also common. WO02/13788 discloses the above-described treatment regime as a “high dose, high energy” regime and it is said to provide a permanent improvement to acne. WO02/13788 additionally discloses a “low dose, low energy” regime that is said to be designed to provide relief from acne. In this treatment 0.1 to 10% wt. ALA acid is applied, and after waiting for the ALA acid to penetrate the skin, is followed by irradiation with a light dose of 1 to 20 J/cm². WO02/13788 suggests that this regime be used in occasional multiple treatments to alleviate acne and be repeated as necessary to maintain diminishment thereof. Although it is recognized that use of such a regime may be pain free, the implication in WO02/13788 is that the therapeutic effect of this treatment regime is less than the high dose, high energy regime it describes and exemplifies.

A need still therefore exists for alternative PDT methods that are free from undesirable side effects (e.g. inflammation) but which have high therapeutic efficacy.

Inflammation and/or erythema is one of the main problems associated with PDT treatment. It is generally believed that inflammation is a necessary element/prerequisite in the cure of AK/BCC/BD by PDT but is not a so big issue for BCCs and BD as the lesions are often small and hidden by clothes. On the opposite AK is located on the face mainly where the need to decrease the downtime is key. A previous, unpublished relation between inflammation and efficacy of PDT is shown in FIG. 1.

A need therefore exists for less inflammatory and still effective methods for treating actinic keratosis and basal cell carcinoma. The present invention addresses that need.

SUMMARY OF THE INVENTION

As is described above, the prior art teaches that inflammation is severe adverse event in the cure of AK and BCC by PDT. However, the present inventors have surprisingly found that application of a photosensitizer for a shorter time period that is classically implemented in a PDT, allows the implementation of a PDT as efficient as in the case where the photosensitizer is used for a longer period of time, greatly reduced side effects usually observed in the prior art PDT protocols, especially inflammation.

Therefore, the invention relates to a PDT treatment, comprising administering to a subject in need thereof a photosensitizer, in particular 5-MAL, for a short duration and then removing the photosensitizer from the skin surface. This PDT protocol is alternatively designated pulse-PDT herein.

Representative photosensitizers include preferably 5-aminolevulinic acid (5-ALA) and derivatives (e.g. an ester) of 5-ALA, more preferably 5-ALA methyl ester (or 5-MAL), or a pharmaceutically acceptable salt thereof. In the present uses and methods, photactivation is achieved by natural or artificial light. In a particular embodiment, the PDT comprises:

-   -   (a) optionally, preparing the area of skin to be treated with         the appropriate pre-treatment, for example a curettage or micro         perforation     -   (b) administering to said animal a composition comprising said         photosensitizer for a short duration; and     -   (c) photoactivating said photosensitizer.

In a particular embodiment, the invention relates to a pulse-PDT treatment, comprising administering to a subject in need thereof a photosensitizer, in particular 5-MAL, for a short duration and then removing the photosensitizer from the skin surface. Photoactivation is then carried out as described throughout the present application. The pulse-PDT treatment of the invention ensures high intracellular PPIX and low extracellular PPIX. Excess amounts of PPIX formation during and after the end of the treatment are thus avoided. In particular, the inventors show that the pulse-PDT treatment of the invention shows less inflammation with unchanged efficacy.

According to an embodiment, the pulse time during which the photosensitizer is let on the skin is comprised between 5 and 120 minutes. According to a preferred embodiment, the pulse time during which the photosensitizer is let on the skin is comprised between 15 and 60 minutes, in particular between 20 and 40 minutes. In a further particular embodiment, the photosensitizer is administered for about 30 minutes (e.g. for 25, 26, 27, 28, 29, 30, 31, 32, 33, 34 or 35 minutes, more particularly during 30 minutes). With such a short photosensitizer treatment, pain level is not changed and PPIX concentration is clearly lower than for the conventional 3 hour exposure to 5-MAL for example, but the treatment is as efficient.

DETAILED DESCRIPTION OF THE INVENTION

Skin Conditions Treated According to the Invention

By the term “animal” is meant herein any human or non-human being. Preferred animals for treatment in accordance with the invention are humans.

According to the present invention, a “skin condition” denotes a disease that can be treated by PDT selected from the group comprising AK and basal cell carcinoma (BCC).

Actinic keratoses (AK) are precancerous (premalignant) skin lesions caused by and associated with chronic exposure to radiant energy, such as sunlight. Actinic keratosis lesions are small, red, rough hyperkeratotic lesions occurring on sun exposed areas of the skin. Actinic keratosis lesions possess many of the same cellular changes observed in a skin cancer called squamous cell carcinoma (SCC). Research shows that a mutated version of the p53 gene is found in sun-damaged cells in the body and is present in more than about 90% of people who have AK and squamous cell carcinomas. Although most actinic keratosis lesions do not actually become cancerous, some lesions can become malignant.

Actinic keratosis develops in skin cells called keratinocytes, which are the cells that constitute about 90% of the epidermis, the outermost layer of skin. Chronic sun exposure, over time, generates mutations in these cells and causes the cells to change in size, shape, the way they are organized, and the way they behave and proliferate. In addition, the proliferation of abnormal cells can even extend to the dermis, the layer of skin beneath the epidermis which is called invasive SCC.

Actinic keratoses (AKs) are common cutaneous lesions associated with chronic exposure to solar ultraviolet radiation (UVR). Frost CA and Green AC, Br J Dermatol 1994; 131:455-64. AKs and squamous cell carcinomas (SCCs) share histologic and molecular features; therefore, AKs are considered by some experts to be incipient SCCs. Cockerell CJ, J Am Acad Dermatol 2000; 42(1 Pt2): 11-17. Although some AKs spontaneously regress and the risk of progression of an individual AK to an invasive SCC is low, AKs tend to be multifocal and recurrent. Since patients who present with multiple AKs may be at higher risk for developing an SCC, treatment of AKs is recommended. Glogau R G, J Am Acad Dermatol 2000; 42 (IPt2):23-24; Criscione V D et al., Cancer 2009:1 15:2523-30; Drake L A et al., J Am Acad Dermatol 1995; 32:95-98.

Actinic keratosis lesions generally measure in size between about 2 to about 7 millimeters in diameter. AK lesions can range in color from skin-toned to reddish and is often hyperkeratotic. On occasion, hyperkeratosis associated with AK lesions will form into the shape of animal horns. When this occurs, the AKs are known as “cutaneous horns”. People who are at higher risk for developing actinic keratosis tend to be fair-skinned and spend significant time outdoors, e.g., at work or at play, over the course of many years. AK lesions usually develop on those areas of the body that have been constantly exposed to the sun for years. Additionally, the skin often becomes wrinkled, mottled, and discolored from chronic sun exposure. Common locations for actinic keratosis include the face, ears, lips, balding scalp, back of the neck, upper chest, the tops of the hands and forearms. When AK lesions develop on the lips, the condition is known as actinic cheilitis. Actinic cheilitis can be characterized by a diffuse scaling on the lower lip that cracks and dries. In some cases, the lips will have a whitish (hyperkeratotic) discoloration on the thickened lip.

Actinic keratosis is generally more common after age 40, because actinic keratosis takes years to develop. However, even younger adults may develop actinic keratosis when living in geographic areas that are exposed to high-intensity sunlight year round, such as Florida and Southern California. AK treatments can be divided into lesion-directed versus field-directed, and provider-administered and patient-administered treatments. In the United States, cryosurgery is the most common provider-administered treatment and is a lesion-directed therapy.

Basal-cell carcinoma (BCC), a skin cancer, is the most common cancer.[1] It rarely metastasizes or kills. However, because it can cause significant destruction and disfigurement by invading surrounding tissues, it is still considered malignant.

Basal-cell carcinomas are differentiated toward the folliculo-sebaceous-apocrine germ, also known as the trichoblast. Overexposure to sun leads to the formation of thymine dimers, a form of DNA damage. While DNA repair removes most UV-induced damage, not all crosslinks are excised. There is, therefore, cumulative DNA damage leading to mutations. Apart from the mutagenesis, overexposure to sunlight depresses the local immune system, possibly decreasing immune surveillance for new tumor cells.

Basal-cell carcinoma also develops as a result of Basal-Cell Nevus Syndrome, or Gorlin Syndrome, which is also characterized by keratocystic odontogenic tumors of the jaw, palmar or plantar (sole of the foot) pits, calcification of the falx cerebri (in the center line of the brain) and rib abnormalities. The cause of the syndrome is a mutation in the PTCH1 tumor-suppressor gene at chromosome 9q22.3, which inhibits the hedgehog signaling pathway. A mutation in the SMO gene, which is also on the hedgehog pathway, also causes basal-cell carcinoma.

Basal-cell carcinomas may be divided into the following types according to Freedberg, et al. (2003). Fitzpatrick's Dermatology in General Medicine. (6th ed.) and James, William D.; Berger, Timothy G.; et al. (2006). Andrews' Diseases of the Skin: clinical Dermatology. Saunders Elsevier:

Nodular basal-cell carcinoma (also known as “Classic basal-cell carcinoma”) is a cutaneous condition, a subtype of basal-cell carcinoma, most commonly occurring on the sun-exposed areas of the head and neck.

Cystic basal-cell carcinoma is a cutaneous condition characterized by dome-shaped, blue-gray cystic nodules.

Cicatricial basal-cell carcinoma (also known as “Morpheaform basal-cell carcinoma,” and “Morphoeic basal-cell carcinoma”) is a cutaneous condition, a subtype of basal-cell carcinoma, and is an aggressive variant with a distinct clinical and histologic appearance.

Infiltrative basal-cell carcinoma is a cutaneous condition which is an aggressive type of basal-cell carcinoma characterized by deep infiltration.

Micronodular basal-cell carcinoma is a cutaneous condition characterized by a micronodular growth pattern.

Superficial basal-cell carcinoma (also known as “Superficial multicentric basal-cell carcinoma”) is a cutaneous condition, a subtype of basal-cell carcinoma, that occurs most commonly on the trunk and appears as an erythematous patch.

Pigmented basal-cell carcinoma is a cutaneous condition, a subtype of basal-cell carcinoma, that exhibits increased melanization.

Rodent ulcer (also known as a “Jacobi ulcer”) is a large skin lesion of nodular basal cell carcinoma with central necrosis and is a type of Basal cell carcinoma

Fibroepithelioma of Pinkus is a cutaneous condition, a subtype of basal cell carcinoma, most commonly occurring on the lower back.

Polypoid basal-cell carcinoma is a cutaneous condition characterized by exophytic nodules (polyp-like structures) on the head and neck.

Pore-like basal-cell carcinoma is a cutaneous condition characterized by a basal-cell carcinoma that resembles an enlarged pore or stellate pit.

Aberrant basal-cell carcinoma is a cutaneous condition characterized by the formation of basal-cell carcinoma in the absence of any apparent carcinogenic factor, occurring in odd sites such as the scrotum, vulva, perineum, nipple, and axilla.

Inflammation is a protective response of cells or tissues to pathogen and external stressful stimuli. During inflammation, the cells or tissues at a site of injury will stimulate the expression of specific genes through NF-kB, followed by an increased expression of chemokines, thereby leading to the accumulation of polynuclear leukocytes, monocytes, macrophages and mast cells at the site of injury (i.e., infiltration). The recruited macrophages will be activated by lipopolysaccharides (LPS) that are expressed on a surface of a pathogen. The activated macrophages will induce the expression of proinflammatory genes (inducing cylooxygenase-2 gene, COX-2, and inducible nitric oxide synthase gene, iNOS) to reinforce inflammatory response. In addition, the activated macrophages release ROS and free radicals to kill pathogens. However, prolonged inflammatory response leads to oxidative stress and damage due to excess accumulation of ROS and free radicals, thereby resulting in chronic inflammation and ultimately potentiating the possibility of chronic illnesses or cancer.

Photosensitizers

Use of 5-ALA (5-amino-4-oxo-pentanoic acid, otherwise known as 5-aminolevulinic acid) and derivatives of 5-ALA in PDT is well known in the scientific and patent literature (see, for example, J. C. Kennedy et al., J. Clin. Laser Med. Surg. (1996)14:289-304, U.S. Pat. No. 5,079,262, U.S. Pat. No. 5,211,938, U.S. Pat. No. 5,234,940, U.S. Pat. No. 5,422,093, U.S. Pat. No. 6,034,267, W091/01727, W096/28412, W02005/092838 and W02006/051269). 5-ALA and all such derivatives of 5-ALA, as well as their pharmaceutically acceptable salts, are suitable for the uses and methods herein described.

The 5-ALA derivatives useful in accordance with the invention may be any derivative of 5-ALA capable of forming protoporphyrin IX (PpIX) or any other photosensitizer (e.g. a PpIX derivative) in vivo. Typically, such derivatives will be a precursor of PpIX or of a PpIX derivative (e.g. a PpIX ester) and which are therefore capable of inducing an accumulation of PpIX at the site to be treated following administration in vivo. Suitable precursors of PpIX or PpIX derivatives include 5-ALA prodrugs which might be able to form 5-ALA in vivo as an intermediate in the biosynthesis of PpIX or which may be converted (e.g. enzymatically) to porphyrins without forming 5-ALA as an intermediate. Esters of 5-aminolevulinic acid and N-substituted derivatives thereof are preferred photosensitizers for use in the invention. Those compounds in which the 5-amino group is unsubstituted (i.e. the ALA esters) are particularly preferred. Such compounds are generally known and described in the literature (see, for example, W096/28412, W002/10120 and W02005/092838 to PhotoCure ASA). Esters of 5-aminolevulinic acid with substituted or unsubstituted alkanols, i.e. alkyl esters are especially preferred photosensitizers for use in the invention. In particular, 5-MAL and 5-MAL derivatives are particularly preferred. Examples of useful derivatives include those of general formula I:

R² ₂N—CH₂COCH₂—CH₂CO—OR¹   (I)

Wherein:

R¹ represents a substituted or unsubstituted straight, branched or cyclic alkyl group (e.g. a substituted or unsubstituted straight-chained alkyl group); and each R² independently represents a hydrogen atom or an optionally substituted alkyl group, e.g. a group R¹; and pharmaceutically acceptable salts thereof.

As used herein, the term “alkyl”, unless stated otherwise, includes any long or short chain, cyclic, straight-chained or branched aliphatic saturated or unsaturated hydrocarbon group. The unsaturated alkyl groups may be mono- or polyunsaturated and include both alkenyl and alkynyl groups. Unless stated otherwise, such groups may contain up to 40 atoms. However, alkyl groups containing up to 30, preferably up to 10, particularly preferably up to 8, especially preferably up to 6, e.g. up to 4 carbon atoms, for example 1, 2, 3 or 4 carbon atoms, are preferred.

The substituted alkyl R¹ and R² groups may be mono or poly-substituted.

Suitable substituents may be selected from hydroxy, alkoxy, acyloxy, alkoxycarbonyloxy, amino, aryl, nitro, oxo, fluoro, —SR3, —NR³ ₂ and —PR³ ₂ groups, and each alkyl group may be optionally interrupted by one or more —O—, —NR³—, —S— or —PR³— groups, in which R³ is a hydrogen atom or a C₁₋₆ alkyl group).

Preferred substituted alkyl R¹ groups include those carrying one or more oxo groups, preferably straight-chained C₄₋₁₂ alkyl (e.g. C₈₋₁₀ alkyl) groups substituted by one, two or three (preferably two or three) oxo groups. Examples of such groups include 3,6-dioxa-1-octyl and 3,6,9-trioxa-1-decyl groups.

Particularly preferred for use in the invention are those compounds of formula I in which at least one R² represents a hydrogen atom. In especially preferred compounds each R² represents a hydrogen atom.

Compounds of formula I in which R¹ represents an unsubstituted alkyl group (preferably C₁₋₈ alkyl, e.g. C₁₋₆ alkyl) or an alkyl group (e.g. C₁₋₂ alkyl, especially C₁ alkyl) substituted by a substituent as hereinbefore defined (e.g. by an aryl group such as phenyl or by an alkoxy group such as methoxy) are also preferred.

Unsubstituted alkyl groups which may be used in the invention include both branched and straight-chained hydrocarbon groups. Compounds of formula I in which R¹ is a C₄₋₈, preferably a C₅₋₈, straight chain alkyl group which is branched by one or more C₁₋₆ (e.g. C₁₋₂ alkyl) groups are preferred. Representative examples of suitable unsubstituted branched alkyl groups include 2-methylpentyl, 4-methylpentyl, 1-ethylbutyl and 3,3-dimethyl-1-butyl. 4-methylpentyl is particularly preferred.

Compounds of formula I in which R¹ is a C₁₋₁₀ straight-chained alkyl group are also preferred. Representative examples of suitable unsubstituted alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl and octyl (e.g. n-propyl, n-butyl, n-pentyl, n-hexyl and n-octyl). Hexyl, especially n-hexyl, is a particularly preferred group. Methyl is also particularly preferred.

Also preferred for use in the invention are those compounds of formula I in which R¹ represents a C₁₋₂alkyl group (preferably a C₁ alkyl group) optionally substituted by an aryl group.

Still further preferred for use in the invention are those compounds of formula I in which R¹ represents an alkyl group (e.g. C₁₋₂ alkyl, especially C₁ alkyl) substituted by an aryl group (e.g. phenyl). Preferred substituted alkyl R¹ groups which may be present in compounds of formula I include C₁₋₆ alkyl, preferably C₁₋₄ alkyl, particularly preferably C₁ or C₂ alkyl (e.g. C₁ alkyl) substituted (preferably terminally substituted) by an optionally substituted aryl group.

By an “aryl group” is meant a group which is aromatic. Preferred aryl groups comprise up to 20 carbon atoms, more preferably up to 12 carbon atoms, for example, 10 or 6 carbon atoms.

Aryl groups which may be present in the compounds of the invention may be heteroaromatic (e.g. 5-7 membered heteroaromatics) but are preferably nonheteroaromatic. By “non-heteroaromatic” is meant an aryl group having an aromatic system comprising electrons originating solely from carbon atoms. Preferred aryl groups include phenyl and napthyl, especially phenyl. In preferred compounds for use in the invention one or two aryl groups may be present, preferably one.

Aryl groups which may be present in the compounds of the invention may optionally be substituted by one or more (e.g. 1 to 5), more preferably one or two, groups (e.g. one group). Preferably the aryl group is substituted at the meta or para position, most preferably the para position. Suitable substituent groups may include haloalkyl (e.g. trifluoromethyl), alkoxy (i.e. —OR groups wherein R is preferably a C₁₋₆ alkyl group), halo (e.g. iodo, bromo, more especially chloro and fluoro), nitro and C₁₋₆ alkyl (preferably C₁₋₄ alkyl). Preferred C₁₋₆ alkyl groups include methyl, isopropyl and t-butyl, particularly methyl. Particularly preferred substituent groups include chloro and nitro. Still more preferably the aryl group is unsubstituted.

In a further preferred aspect the invention provides the use of a photosensitiser which is a compound of formula I wherein R¹ represents an aryl substituted C₁₋₄ alkyl group (preferably C₁₋₂, e.g. C₁), preferably wherein said aryl group comprises up to 20 carbon atoms (e.g. up to 12 carbon atoms, especially 6 carbon atoms) and is itself optionally substituted, and each R² is as hereinbefore described.

Preferred compounds for use in the invention include methyl ALA ester, ethyl ALA ester, propyl ALA ester, butyl ALA ester, pentyl ALA ester, hexyl ALA ester, octyl ALA ester, 2-methoxyethyl ALA ester, 2-methylpentyl ALA ester, 4-methylpentyl ALA ester, 1-ethylbutyl ALA ester, 3,3-dimethyl-1-butyl ALA ester, benzyl ALA ester, 4-isopropylbenzyl ALA ester, 4-methylbenzyl ALA ester, 2-methylbenzyl ALA ester, 3-methylbenzyl ALA ester, 4-[t-butyl]benzyl ALA ester, 4-[trifluoromethyl]benzyl ALA ester, 4-methoxybenzyl ALA ester, 3,4-[dichloro]benzyl ALA ester, 4-chlorobenzyl ALA ester, 4-fluorobenzyl ALA ester, 2-fluorobenzyl ALA ester, 3-fluorobenzyl ALA ester, 2,3,4,5,6-pentafluorobenzyl ALA ester, 3-nitrobenzyl ALA ester, 4-nitrobenzyl ALA ester, 2-phenylethyl ALA ester, 4-phenylbutyl ALA ester, 3-pyridinyl-methyl ALA ester, 4-diphenyl-methyl ALA ester and benzyl-5-[(1-acetyloxyethoxy)-carbonyl]amino levulinate.

Still further preferred compounds for use in the invention include methyl ALA ester, ethyl ALA ester, 2-methoxyethyl ALA ester, benzyl ALA ester, 4-isopropylbenzyl ALA ester, 4-methylbenzyl ALA ester, 2-methyl benzyl ALA ester, 3-methyl benzyl ALA ester, 4[t-butyl]benzyl ALA ester, 4-[trifluoromethyl]benzyl ALA ester, 4-methoxybenzyl ALA ester, 3,4[di-chloro]benzyl ALA ester, 4-chlorobenzyl ALA ester, 4-fluorobenzyl ALA ester, 2-fluorobenzyl ALA ester, 3-fluorobenzyl ALA ester, 4-nitrobenzyl ALA ester, 2-phenylethyl ALA ester, 4-phenylbutyl ALA ester, 3-pyridinyl-methyl ALA ester, 4-diphenyl-methyl ALA ester and benzyl-5-[(1-acetyloxyethoxy)-carbonyl]amino levulinate.

Particularly preferred compounds for use in the invention include methyl ALA ester, hexyl ALA ester and benzyl ALA ester, especially methyl ALA ester.

The compounds for use in the invention may be prepared by any conventional procedure available in the art (e.g. as described in WO02/10120 to PhotoCure ASA). For example, esters of 5-ALA may be prepared by reaction of 5-ALA with the appropriate alcohol in the presence of acid. Alternatively compounds for use in the invention may be available commercially (e.g. from Photocure ASA, Norway).

Photoactivation

According to the present invention, photoactivation is achieved by either an artificial or natural light source. In a preferred embodiment, photoactivation of the photosensitizer is achieve by LED or sunlight.

Light Sources—Artificial

Electroluminescence (EL) is an optical and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field. This is distinct from black body light emission resulting from heat (incandescence), from a chemical reaction (chemiluminescence), sound (sonoluminescence), or other mechanical action (mechanoluminescence).

Among the electroluminescence sources, LED (Light emitting diodes) lamps are well known and preferred as artificial light souce in the present invention. A LED lamp (LED light bulb) is a solid-state lamp that uses light-emitting diodes (LEDs) as the source of light. The LEDs involved may be conventional semiconductor light-emitting diodes, organic LEDs (OLED), or polymer light-emitting diodes (PLED) devices.

The LED lamps used in the examples hereafter are defined by some characteristics like wavelength (in nm), power of the LED (in mW/cm²) energy of the LED (in J/cm²). Such particular features are provided below.

Light Sources—Natural

This aspect of the invention includes photoactivation with either natural sunlight or any light source which provides artificial sunlight (i.e. the entire range from UV to IR). Use of natural sunlight as the light source has the advantage that the animal being treated is free to leave the clinical environment where treatment is normally conducted.

Light Sources—Intensity

In the uses and methods of the invention, photoactivation may be achieved using light sources known in the art. Methods for the irradiation of different areas of the body, e.g. by lamps or lasers are well known in the art (see for example Van den Bergh, Chemistry in Britain, May 1986 p. 430-439). The wavelength of light used for irradiation may be selected to achieve a more efficacious photosensitizing effect. The most effective light is light in the wavelength range 300-800 nm, typically within the 400-700 nm range. The irradiation will in general be applied at a dose level of 30 to 200 Joules/cm², for example at 100 Joules/cm². A light source having a fluence rate of 1 to 100 mW/cm² may be used.

In particularly preferred uses and methods of the invention, side effects of PDT are further prevented or reduced by photoactivating with a light source having a fluence rate of less than 50 mW/cm².

Still more preferably the irradiation is applied at a dose of 10 to 100 J/cm², more preferably 20 to 60 J/cm², e.g. about 37 Joules/cm². Penetration of light into tissues depends on the wavelength used and is deeper for red light than for blue light.

Irradiation with an artificial light is preferably performed for 1 to 30 minutes, preferably for 1 to 15 minutes, more preferably from 5 to 10 minutes, preferably for 5 minutes, depending on the light dose and fluence rate. A single irradiation may be used or alternatively a light split dose in which the light dose is delivered in a number of fractions, e.g. a 1 to 10 minutes between irradiations, may be used.

Photoactivation with natural light is preferably done for a duration between 30 minutes and 3 hours.

Treatment of the Skin According to the Invention

The methods and uses of the invention may involve pretreatment of the skin. For example, the pretreatment may comprise curettage, dermoabrasion (e.g. with sandpaper) or micro-perforation before application of the photosensitizer. In a particular embodiment, the pretreatment includes perforation of the skin using an adapted device such as a micro-needling device, for example a dermaroller.

The methods and uses of the invention may also be carried out with or without occlusion, more preferably with occlusion.

The photosensitizer is applied as a pulse therapy for the time periods provided above, for example for a duration of about 30 minutes. The inventors herein show that such a pulse therapy has the advantage of being as efficient as therapy with longer exposures, but with less PPIX produced, thereby preventing side effects associated with PPIX.

Photoactivation is performed after application of the photosensitizer, preferably after having removed the photosensitizer from the skin.

In a particular embodiment, the treatment comprises:

-   -   (a) optionally, preparing the area of skin to be treated with         the appropriate pre-treatment, for example a curettage or micro         perforation, in particular a perforation with an adapted device         micro-needling device such as a dermaroller;     -   (b) administering to said animal a composition comprising said         photosensitizer for a short period of time;     -   (c) optionally, removing the photosensitizer; an     -   (c) photoactivating said photosensitizer.

In an embodiment of the invention, the pulse photodynamic therapy (PDT) on an animal comprises:

-   -   a) administering to said animal a composition comprising said         photosensitizer for a duration between 5 min to 120 minutes;     -   b) optionally, removing the photosensitizer; and     -   c) photoactivating said photosensitizer for a duration between 1         to 15 minutes with artificial light or 0.5 hour to 3 hours with         natural light.

In a more preferred embodiment of the invention the use of a photosensitizer in photodynamic therapy (PDT) on an animal comprises:

-   -   a) administering to said animal a composition comprising said         photosensitizer for a duration between 15 min to 60 minutes;     -   b) optionally, removing the photosensitizer; and     -   c) photoactivating said photosensitizer for a duration between 5         to 10 minutes with artificial light or 0.5 hour to 2 hours with         natural light.

In a more preferred embodiment of the invention the photosensitizer for use in photodynamic therapy (PDT) on an animal comprises

-   -   a) administering to said animal a composition comprising said         photosensitizer for a duration of 30 minutes; and     -   b) optionally, removing the photosensitizer; and     -   c) photoactivating said photosensitizer 2.5 hours later for a         duration of 9 minutes with artificial light or of at least 2         hours with natural light.

Any of the above particular or preferred embodiments may comprise a step of pretreating the skin as described above, before the step of applying the photosensitizer on the skin.

Furthermore, in a particular embodiment, the PDT according to the invention also comprises applying to the skin of the subject a glucocorticosteroid. According to this embodiment, the glucocorticosteroid is administered for further preventing or reducing the side effects associated with PDT. The glucocorticosteroid may be applied either simultaneously, before, after or both before and after administration of the photosensitizer. In a particular embodiment, the glucocorticosteroid is selected from the group consisting of Clobetasol propionate, Betamethasone dipropionate, Halobetasol proprionate, Diflorasone diacetate, Diflucortolone valerate, Hydrocortisone 17-butyrate, Mometasone furoate, Methylprednisolone aceponate and Halometasone. In a further particular embodiment, the glucocorticosteroid is Clobetasol propionate or Betamethasone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the inflammation vs. response rate (3 months) of AK on the face.

FIG. 2 is a graph showing the mean increased redness the day after PDT.

FIG. 3 is a graph reporting the visual redness 1 day after PDT with different treatment protocols.

FIG. 4 is a graph showing the pain scale after different treatments.

FIG. 5 is a graph showing the cure rate after different treatments.

FIG. 6 is a graph showing the increase in erythema percentage one day after treatment with different protocols.

FIG. 7 s a graph showing erythema scale after treatment with different protocols.

FIG. 8 is a graph showing the mean photobleaching in the standard treatment and a different “pulse” treatment.

FIG. 9 is a graph showing the inflammation (erythema)/PpIX formation relationship

EXAMPLES Example 1 PDT Procedure Change to Minimize Inflammation in PDT

According to the just mentioned theory it would be preferable to keep PPIX and cellular enzymes away from the extracellular compartment, thereby avoiding inflammation.

The purpose of this project is therefore to keep the PPIX formation within the mitochondria and avoid excess amounts of PPIX to be formed. Simultaneously PPIX should be allowed to be formed for such a long time that most unnormal cells will be affected.

So the purpose of PDT is to kill unnormal cells, preferably by apoptosis. The ideal situation would be to keep PPIX inside the cell and to destroy the mitochondria only, thereby inhibiting the ATP formation necessary for cell functions. That should result in cell death by apoptosis.

One possible way to achieve this would be to give a short 5-MAL pulse treatment to get a high concentration of 5-MAL in the cells initially and then diminish further access to 5-MAL by removing 5-MAL from the skin surface.

This could be done by only exposing the skin to 5-MAL for a short time, after which all 5-MAL is removed from the skin surface. If the right “pulse time” can be found it might ensure high cellular PPIX and low extracellular PPIX. Excess amounts of PPIX formation during and after the end of the treatment would thus be avoided.

The result shows less inflammation with unchanged efficacy and thus mitochondria destruction seems to be the most important factor in PDT.

To estimate the preferable Metvix “pulse time” a separate investigation was performed (Method B) on 24 healthy volunteers. The pulse time was 20 min., 40 min., 60 min., and the conventional 180 min, after which excess amounts of Metvix was removed from the skin.

The formation of PPIX after 3 hours is seen in FIG. 8, and the relation to inflammation is seen in FIG. 9. It is seen that PPIX concentration speeds up between 20-40 min. of “pulse exposure”, and so we have chosen 30 min. as the minimum “pulse exposure” time in the following (Method A) investigation of efficacy and inflammation by this method change. The results are illustrated in Column 3 in FIGS. 4, 5, 6, and 7. The procedure change clearly diminishes inflammation (erythema), without affecting the cure rate (FIG. 5). Pain level is not changed. PPIX concentration is clearly lower than for the conventional 3-hour exposure to Metvix (Table 1 and FIG. 8).

Methods

Healthy Volunteers

Twenty-four healthy male volunteers of Scandinavian ancestry were included in the study (mean age 30 years, range 20-51). A treatment area was selected on the inside of both forearms of the volunteer. Each treatment area was divided into four minor treatment fields of the size 2×5 cm with at least 3 cm between each field using a prefabricated flexible template. In order to imitate skin lesions all fields were tape stripped 10 times with occlusive dressing before treatment (Tegaderm™ Roll, 3M, Glostrup, Denmark).

On the left forearm vehicle Unguentum M was applied to the treatment field.

On the right forearm excess amounts of 5-MAL 16 % (Metvix®, Photocure, Oslo, Norway) were applied to all four fields of treatment. All fields were covered with light-impermeable, occlusive dressing. After 20 minutes the dressing was removed from the first field and the excess cream gently wiped off. The field was covered again with a thin piece of gauze and light impermeable dressing. After additional 20 and 40 min same procedure was followed with the second and third field. 180 min after application of 5-MAL and vehicle was removed from all five fields, and the excess cream was gently wiped of the last field. All fields were illuminated with red light. Illumination was performed with red LED light 630 nm peak (Aktilite™ 128; Photocure ASA, Oslo Norway) using a total light dose of 37 J/cm² given over 9 min. During and after illumination pain was recorded. The volunteers were equipped with a special diary for recording pain in the days after treatment. Four follow-up visits were performed at day 1,2,3 and 8 after treatment.

PpIX Fluorescence

5-MAL-induced PpIX fluorescence was depicted non-invasively using a fluorescence camera (Medeikonos AB, Gothenburg, Sweden). The amount of PpIX fluorescence was calculated from the photographs by the program MatLab® (MatLab®, MathWorks, Natic, US). The amount of fluorescence was measured before tape stripping and cream application (baseline) and before and after illumination.

The photo bleaching is then the difference in PpIX fluorescence (AU) calculated from the pre and post illumination images.

Erythema and Pigmentation

As an indicator of inflammation erythema was measured. The erythema was assessed by an expert evaluator and measured objectively.

The objective measurements of erythema and pigmentation were performed using a skin reflectance meter (Optimize Scientific 558, Chromo-Light, Espergaerde, Denmark).

Erythema % and pigmentation % were measured before treatment, immediately before illumination, immediately after illumination, and at the four follow-up visits.

Pain Score

The volunteers scored their pain every minute during illumination, and recorded their pain in the diary every hour after illumination on the treatment day, twice per day the next three days and once a day on the following five days. Since PDT was performed at different times of the day the number of evaluations differed from 3 to 11 the first day. Pain was assessed using a numerical scale ranging from 0 to 10, where 0 is no pain and 10 is worst imaginable pain. To make it easier for the patients to identify the different treated fields, the dairy was supplied with numbered drawings of the fields.

Randomizing

The study was designed as an open randomised trial. A statistical adviser made the randomisation. Since the sequence of treatment duration was predefined, randomization was only determining which of the four treatment fields should be the first.

Statistics

The sample size was calculated on the bases of data from the literature. We set the minimal clinical relevant difference to 8.8 % (50% of the earlier found 17.6%) and choose a power of 0.80 and a significance level of 0.05, 22 volunteers should be included.

To identify differences in pain score, erythema% and pigmentation% between the treatment fields we used Wilcoxon Signed Ranked Test, since all results were paired.

For all calculations a p-value <0.05 was considered statistical significant. All analyses were performed with PASW Statistics 19.0 for Windows (SPSS Inc, Chicago, Ill., USA). 

1. A method of treating a skin condition in an animal the method comprising adminisering a photosensitizer to the animal skin, wherein the photosensitizer treats the skin condition with photodynamic therapy (PDT), and wherein the photosensitizer is applied to the skin of the animal for a short period of time, and the skin condition is actinic keratosis or basal cell carcinoma.
 2. The method according to claim 1, wherein the method reduces side effects associated with PDT.
 3. The method according to claim 1, further comprising applying the photosensitizer to the skin of the animal for a period of from 5 minutes to 120 minutes.
 4. The method according to claim 1, wherein the PDT includes a photoactivation achieved by artificial or natural light source.
 5. The method according to claim 1, wherein the PDT comprises: a) administering to the animal a composition comprising the photosensitizer for a duration of from 5 minutes to 120 minutes; and b) photoactivating the photosensitizer for a duration of from 1 minute to 15 minutes with artificial light or from 0.5 hour to 3 hours with natural light.
 6. The method according to claim 5, wherein the PDT comprises: a) administering to the animal a composition comprising the photosensitizer for a duration of from 15 minutes to 60 minutes; and b) photoactivating the photosensitizer for a duration of from 5 minutes to 10 minutes with artificial light or from 0.5 hour to 2 hours with natural light.
 7. The method according to claim 6, wherein PDT comprises: a) administering to the animal a composition comprising the photosensitizer for a duration of 30 minutes; and b) removing the photosensitizer; and c) photoactivating the photosensitizer 2.5 hours later for a duration of 9 minutes with artificial light or of at least 2 hours with natural light.
 8. The method according to claim 1, wherein the photosensitizer is selected from the group consisting of 5-ALA, 5-ALA derivatives, 5-MAL, 5-MAL derivatives, and compounds covered by general formula I: R² ₂N—CH₂COCH₂—CH₂CO—OR¹   (I) wherein: R¹ represents a substituted or unsubstituted straight, branched or cyclic alkyl group; and each R² independently represents a hydrogen atom or an optionally substituted alkyl group; and pharmaceutically acceptable salts thereof.
 9. The method according to claim 1, wherein the photosensitizer is 5-ALA or 5-methyl ALA ester.
 10. The method according to claim 1, wherein administering the photosensitizer to the animal is carried out with or without occlusion.
 11. The method according to claim 1, wherein the photosensitizer is used in combination with a glucocorticosteroid.
 12. The method according to claim 3, wherein the period of time is from 15 minutes to 60 minutes.
 13. The method according to claim 4, wherein the artificial or natural light source is a LED or sunlight.
 14. The method according to claim 8, wherein the alkyl group is a substituted or unsubstituted straight-chained alkyl group.
 15. The method according to claim 10, wherein the administration of the photosensitizer is carried out with occlusion. 